LOPA — Layer of Protection Analysis and IPL Credit Rules

LOPA is where a HAZOP scenario becomes a number that decides whether a SIF is needed and at what SIL. The method is simple; the mistakes are in the details — initiating-event frequencies taken from the wrong table, safeguards credited that are not independent, conditional modifiers applied twice, tolerable-frequency criteria nobody has agreed. The course works through scenario selection, frequency and probability data, IPL qualification rules and documentation, then runs ten scenarios from real HAZOP worksheets.

• Select LOPA scenarios from a HAZOP and define them with a single cause and consequence
• Assign initiating-event frequencies from recognised data sources and site history
• Apply the independence, effectiveness, auditability and specificity tests before crediting an IPL
• Credit BPCS loops, alarms with operator response, relief devices and mitigation layers correctly
• Use enabling conditions and conditional modifiers without double counting
• Set tolerable-frequency targets and derive SIL targets and gap-closure options